1. Field of the Invention
The invention is related to the field of magnetic disk polishing to remove asperities such that the data storage capabilities of magnetic disk drive systems may be increased.
2. Statement of the Problem
To keep up with the demand for increased magnetic data storage density, smoother magnetic disk surfaces are used to avoid interference with read/write heads and the magnetic disks. Generally, the magnetic layers and carbon overcoat of a thin film magnetic disk are vacuum deposited to protect the magnetic layers from corrosion. The disk is then coated with about 1 nm of lubricant and polished with a mild abrasive tape, such as an alumina composite abrasive layer on a Mylar film, to remove asperities (e.g., above 5 nm). A polishing pad is used to press the polishing tape onto a surface of the magnetic disk. For example, the polishing pad may be applied to the back of the Mylar film to ensure that the abrasive composite layer contacts the magnetic disk surface. Polishing, however, is a delicate process as it can damage a magnetic disk by scratching the 2 to 4 nm thick carbon overcoat or the magnetic layers below.
A soft elastomeric pad that has a relatively low loss tangent can improve polishing and disk yield because the pad is more apt to “track” a disk's “waviness”. For example, the low modulus of the soft elastomeric pad allows the pad to more intimately contact the polishing tape when compared to the more conventional urethane foam pad, or “foam rubber” pad. The soft elastomeric pad may be injection molded from a thermoplastic elastomer (TPE), such as a block copolymer of styrene-ethylene/butylene-styrene or styrene-ethylene/propylene-styrene. However, there is a strong adhesion between the smooth Mylar tape and a smooth pad, because the lightly cross linked elastomeric pad intimately contacts the Mylar film. For example, when a soft material is pressed into contact with a flat surface, a strong adhesion force arises due to dispersion interaction energy. During the automated disk polishing process, the pad is intermittently pressed onto the back of the tape and then retracted from the tape at the end of the disk polishing process. A relatively strong adhesion between the pad and the back of the tape causes a section of the tape between guide rollers to be “pulled” with the pad when the pad is retracted. This tape deflection continues until the tape tension force exceeds the adhesion force, at which point the tape abruptly releases and snaps back to its centered position.
The tape deflection and sudden release of the tape is undesirable because the polishing tape contains an alumina particle composite binder as well as other particles that have been removed from the disk. The vibration of the tape in close proximity to the disk may therefore detach abrasive particles from the tape into the air during manufacturing potentially scratching the disks. Accordingly, there exists a need to polish magnetic disks in a manner that substantially reduces disk asperities while preventing tape deflection during the polishing process.